Adenylate Kinase from Bakers' Yeast

Studies of equilibrium exchange rates showed that the ATP-AMP phosphotransferase (EC 2.7.4.3), yeast adenylate kinase, reaction was of a random order. The rates of exchange of AMP and ATP with ADP under similar conditions were very nearly equal. A double reciprocal plot of the exchange rate against the ATP concentration yielded a minimum dissociation constant of the same order as the Km value for ATP. These data served as indications of a random mechanism. An experiment with the use of 14C- and 32P-labeled nucleotides in equilibrium exchange studies revealed that the rate-limiting step of the reaction was the interconversion of the ternary complex and not the binding of substrates or the dissociation of products. The equilibrium concentrations of the adenosine and deoxyadenosine 5'-phosphates were also determined at various pH values, magnesium ion concentrations, and temperatures.